Variable blockage flame stabilizer



VARIABLE BLOCKAGE FLAME STABILIZER Filed Jan. 15, 1958 INVENTORS. JflMt-a E WOEJAWM BY #9801 0/4 672-710" United States Patent 2,936,585 VARIABLE BLOCKAGE FLAME STABILIZER James E. Worsham, Glendale, Ohio, and Harold H. Stent,

Philadelphia, Pa., assignors to General Electric Company, a corporation of New York Application January 15, 1958, Serial No. 709,111

3 Claims. (Cl. 60-49-72) The present invention relates to a variable blockage flame stabilizer for turbo-jet engine afterburners and more particularly to a variable blockage flame stabilizer which is adjustable to provide variable turbulence characteristics.

As a means of increasing the thrust of a turbo-jet englue, it has been common practice to inject and burn additional fuel in the gas stream flowing from the turbine. Since the velocity of the gas stream normally exceeds the speed of flame propagation of conventional fuels, means has been provided for blocking a portion of the afterburner duct to produce local stagnation of the gas stream in order to maintain a suitable flame formation. It has been conventional practice in turbo-jet engines employing an afterburner to provide a bluff body permanently mounted within the afterburner duct to provide blockage of the duct and form a region of turbulence or recirculating flow in which a flame can be stabilized, to provide pilot for the ignition of the high velocity fuel-air mixture. Blockage is usually obtained by means of a grid of V-shaped members or gutters positioned with the apex. of the VS pointing upstream. The V-gutters conventionally used for this purpose are efficient in creating turbulence during afterburner operation, but have the disadvantage that they also cause high total pressure losses when the afterburner is not in use, thus detracting from the overall efi'iciency of the engine. A further disadavntage in V-gutters arises in the case of engines which employ both conventional and high energy fuels, because of the variation in physical properties (i.e., flame speed) of the different fuels. Since the optimum included angle of a V-gutter varies with flame speed, the V-gutter which gives maximum combustion efliciency with one fuel will be far from optimum with a second fuel.

Adjustable flame stabilizers have been suggested in an attempt to provide maximum combustion efliciency during afterburner operation and minimum total pressure loss during normal engine operation. The adjustable flame stabilizers heretofore known have been of two general types, in that in their inoperative position, they are either, (1). pivoted or folded parallel to the gas path, or are (2) retracted into the tailcone of the engine or the Walls of the afterburner duct. In the first case, the upstream edges of the device interfere with the smooth flow of the propulsive gases and cause appreciable total pressure losses. In the second case, the retracting and extending mechanisms are heavy and are expensive to build and maintain because of the high temperatures to which they are exposed within the afterburner duct. In addition, both types of previously known adjustable flame stabilizers have had only two positions, i.e., fully operative or fully inoperative, and have not been adjustable between these two positions to provide variable turbulent characteristics. i i

An object of the present invention is the provision of an improved afterburner flame stabilizer.

Another object is the provision of a variable blockage flame stabilizer which is adjustable to give maximum 2,936,585 Patented May 17, 1960 combustion efliciency during afterburner operation and minimum total pressure loss during non-afterburner use.

A further object is the provision of a variable blockage flame stabilizer which is adjustable to give variable turbulence characteristics.

An additional object is the provision of an improved afterburner flame stabilizer adapted for use with turbojet engines employing both conventional and high energy fuels.

The present invention overcomes the disadvantages of prior known adjustable flame stabilizers by the provision of a variable blockage flame stabilizer which is adjustable to provide maximum combustion efliciency during afterbumer operation, minimum total pressure loss during normal engine operation, and variable turbulence characteristics for optimum use with various fuels. This is accomplished by the provision of a strut supporting means adapted to extend diametrically across an afterburner duct, a plurality of thin planar flame stabilizer elements projecting transversely from the strut in opposite directions and spaced apart over the length of the strut, and means for adjusting the angle of attack of the flame stabilizer elements relative to the direction of flow of the gas stream.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

Referring more particularly to the drawing,

Fig. l is a side view partly in section of the variable blockage flame stabilizer of the present invention mounted in an afterburner duct;

Fig. 2 is a front view of the present invention in its maximum blockage position;

Fig. 3 is a sectional view taken along lines 3-3 of Fig. 2;

Fig. 4 is a sectional view at an enlarged scale taken along lines 4-4 of Fig. 2;

Fig. 5 is a perspective view of an actuating mechanism suitable for use with the variable blockage flame stabilizer of the present invention;

Fig. 6 is a perspective view of an alternative actuating mechanism; and

Fig. 7 is a front view of another embodiment of a variable blockage flame stabilizer employing a third actuating means.

Referring more particularly to the drawing, Fig. 1 shows a variable blockage flame stabilizer 11 according to the present invention mounted downstream of tailcone 16 and fuel spraybars 17 in the afterburner duct 12 of a. turbo-jet engine. The variable blockage flame stabilizer itself, as shown in Fig. 2, is comprised of a center post or strut .13 which extends diametrically across the tailpipe and is secured thereto at its opposite ends, and a plurality of pairs of thin planar flame stabilizer elements 14 and 15 supported by the strut 13 in spaced relation and projecting transversely of the strut in opposite directions, with their extremities in close proximity to the walls of theduct 12. As illustrated in Fig. l, the flame stabilizer in its minimum blockage position has the narrowest dimension of the stabilizer elements presented to the flow of propulsive gases. This is the position usually selected for normal engine operation when the afterburner is not in use. The maximum blockage position, wherein the widest dimension of the stabilizer elements is at right ass-a, use:

ingsI19 and 21.. The. strut 13 is hollow and enclosesa- 18, a worm gear 23 which meshes with spur gear 22, and

actuator: (not shown) and is drivingly connected to the.

gears22 by means of a chain 29.

Asecond structural embodiment of a variable blockage flame stabilizer according to the present invention is shown in Fig. 7 andincludes a center post or strut 32 and spaced oppositely extending stabilizer elements 33 and 34. In this modification the stabilizer elements are connected in pairs by rods 35 which aresupported at their midpoints by the strut 32, while the opposite ends of the rods are journalled in the wall of the afterburner duct as at 36 and 37. An actuator 38 is connected to one end of each of the rods and each of the actuators is. operatively connected to a control 39 which selectively energizes the actuators to position the pairs of stabilizer elements. In this embodiment each pair of stabilizer elements may be positioned independently of the remaining pairsof elements to give varying'amounts of blockage in different parts of the gas path. In some cases, where the gas pressures are not excessive, the center post or strut 32 may be omitted and the stabilizer elements 33 and 34formed as a unitary member.

As can be seen'from the above discussions, the variable blockage flame stabilizer of the present invention operates ina very simplemanner to give optimum blockage of the afterburner duct during afterburner operation and minimumblockage of the duct when the afterburner is not in use. Since the center strut is of streamlined airfoil configuration and since the stabilizer elements are either flat plates with rounded leading edges or are of streamlined airfoil cross-section, the present flame stabilizer causes very little, if any, total pressure loss during normal engine operation. Also, since the present flame stabilizer is not retracted, but is in position within the afterburner duct at all times, the stabilizer elements are: capable of being-adjusted to various positions between the minimum and maximum blockage positions to provide variable turbulence characteristics. In addition to the varying amount of blockage for afterburner and non-afterburner operation with conventional fuels, the present construction permits the use of a slight amount of blockage for enhanced mixing of high energy fuels to increase the flame spreading, even though, because of the higher flame speed of such fuels, flame stability itself is no problem.

For afterburner operation with conventional fuels, tests have demonstrated that the optimum stabilization of flame is achieved in most instances when the-stabilizer elements are adjusted so that their widest dimension forms an angle of from 45 to 60 degrees with the minimum blockage position. However, there maybe instances, such as during light off of the afterburner, when themaximum blockage may be desirable.

The specific dimensions of a given flame stabilizer are functions of the particular design and may vary from one application to another. However, a typical application mightbe for stabilizer elements of from 1" to 1 /2 in width laid out so that approximately 30%v of the duct area is occupied by the elements. For designsimplicity all of-the stabilizer elements may be turned in the same direction. However, in particular applications it may be An alternative form of actuating means is' the flowing gases.

4 advisable to turn some of the elements in one-direction and others in the opposite direction. This can be accomplished in the embodiment of Fig. 7 by means of control 39 and in the embodiment of Figs. 4 and 5 by reversing the direction of threads on selected worm gears 23.

While the primary advantage of the present variable blockage flame stabilizer over prior art flame stabilizers.

resides in its adjustability to permit maximum efficiency ofengine operation under various conditions and with.

various fuels, the tin stabilizer elements used in the embodiments illustrated present an additional advantage over conventional flameholder practice. A thin flat plate or airfoil at an angle of 45 degrees or greater with the minimum blockage position affords a greater area of reduced velocity and transverse turbulence in its wake than a V-gutter of equal width. Since the stabilizer elements of the present construction require .less material and are lighter in weight than a V-gutter of equal width, theyper mit savings in cost and weight while providing improved flame stabilization. The thin' planar stabilizer elements have a further advantage in the case of high energy fuels since their entire upper and lower surfaces are swept by 7 Thus, no dead spots or sheltered areas are formed adjacent their downstream edges for the growth of products of combustion or similar deposits de rived from such fuels.

While particular embodiments of the invention have been illustrated and described, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from the invention and it is intended to cover in the appended claims all such changes and modifications that come within the true spirit and scope of the invention.

What we claim as new and desire to secure by Letters Patent of theU.S. is:

l. A variable blockage flame stabilizer for usein an.

afterburner of a turbo-jet engine, comprising: a hollow elongated strut of streamlined cross-section; a plurality of thin elongated stabilizer elements supported by saidstrut and'projecting laterally therefrom in opposite directions, said elements being spaced apart over the length of the strut; and actuating means operatively connected to each of said elements for selective rotation of said elements about their longitudinal axes.

2. In combination with the tailpipe of a turbo-jet engine, a variable blockage flame stabilizer comprising: an.

elongated strut of streamlined cross-section extending dimetrically across the tailpipe with its opposite extremities secured thereto; a plurality of thin elongated stabilizer elements supported in pairs by said strut and pro.- jecting laterally therefrom in opposite directions with their outer extremities adjacent walls of said tailpipe, said elements being spaced apart over the length of the strut;. journal means carried by said walls and supporting said ators being selectively operable for independent rotationv of said pairs of elements.

References Cited in the file of this patent UNITED STATES PATENTS 2,607,452 Hall Aug. 19, 1952. 2,835,108 Karen May 20, 1958 FOREIGN PATENTS 510,584- Canada ..a Mar; 1', 1955 i anna 

